The objective of this proposal is to investigate the functional significance of correlated neuronal discharges in the cat retina. Traditionally, retinal ganglion cells are thought to transmit neural messages by independently modulating their firing rates, yet we also know that groups of cells can fire nerve impulses at nearly the same time. Whether these synchronous firing events are important for transmitting visual information or merely an epiphenomenon of retinal wiring remains an open question. I propose to record simultaneously from ganglion-cell bodies and optic-tract fibers in vivo while stimulating the retina of cats with patterns varying in space and time. The firing events should be stimulus dependent if they are at all relevant to cat vision. The specific aims are: 1) To determine the optimal stimulus for correlating the discharges of cat retinal ganglion cells in vivo. 2) To measure the strength of correlation of ganglion-cell discharges evoked by the optimal stimulus. The results will eliminate one or more of the following hypotheses about correlated discharges: they encode distinct neural messages, link stimulus features in space, or are a remnant of retinal development.